A driveline may include a disconnect clutch that is combined with a torque converter and located between an engine and the torque convertor to selectively couple the engine to the torque converter. The disconnect clutch may allow engine rotation to stop while a vehicle is moving without being powered from an adjustable torque source. For example, the engine may be stopped when the vehicle is coasting down a road having a negative grade. The torque converter dampens driveline torque and provides torque multiplication since the torque converter input (e.g., torque convertor impeller) may rotate at a different speed than the torque converter output (e.g., torque converter turbine). Thus, the output side of the disconnect clutch may rotate at a speed different than the transmission input shaft speed. The engine may be stopped to conserve fuel and reduce an amount of air pumped through an exhaust after treatment device coupled to the engine while the vehicle is moving. However, if the engine is restarted, it may be difficult to control closing of the driveline disconnect clutch because packaging constraints may not allow a speed sensor to be placed at the output side of the disconnect clutch. Consequently, it may be difficult to control torque flow through the disconnect clutch when the engine is being recoupled to the torque converter impeller.
The inventors herein have recognized the above-mentioned issues and have developed a method for operating a driveline, comprising: at least partially closing a torque converter clutch in response to a request to open a disconnect clutch, the torque converter clutch at least partially closed before opening the disconnect clutch; and accelerating an engine that has stopped rotating to a speed based on disconnect clutch output side speed.
By at least partially closing a torque converter clutch before opening a disconnect clutch, speed of an output side of a driveline disconnect clutch may be determined based on speed of a transmission shaft. In particular, closing the torque converter clutch may cause the torque converter impeller to rotate at a same speed as a torque converter turbine. The torque converter turbine rotates at a same speed as a transmission input shaft. Consequently, the driveline disconnect clutch output speed may be determined from the transmission input shaft speed which may be monitored via a speed sensor. Additionally, closing the torque converter clutch allows a transmission pump to be rotated via torque from the torque converter impeller. As a result, the transmission pump may supply pressure to operate transmission clutches even though the engine is not rotating the torque converter impeller which is mechanically coupled to the transmission pump.
The present description may provide several advantages. For example, the approach may reduce vehicle fuel consumption by allowing an engine to stop while a vehicle in which the engine operates is moving. Additionally, the approach may allow transmission shifting to maintain pump output pressure while an engine has stopped rotating. Further, the approach may extend vehicle coasting, thereby reducing fuel consumption.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.